Selective-sampling receiver

ABSTRACT

A receiver that selectively samples a received signal in order to suppress an interference component of the signal while recovering a desired component. The selective sampling may be accomplished by low cost, low complex analog or digital circuitry. The receiver includes a first input that receives a first signal, including a desired signal component and an interference signal component and a second input that receives a second signal including the interference component only. The first and second signals are then provided to the sampling circuitry. First, the phase of the interference component of the both the first and second signals is aligned. Next, the points in a wave cycle that the second signal is at a power minimum are detected. Finally, first signal is sampled close to the point when the second signal is at the power minimum to recover the desired signal component and suppress the interference component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part of U.S. patent applicationSer. No. 11/186,712, entitled SELECTIVE-SAMPLING RECEIVER and filed Jul.21, 2005, which application claims the benefit of U.S. ProvisionalPatent Application Ser. No. 60/590,095, filed Jul. 22, 2004. Theforegoing applications are incorporated herein in their entirety by thisreference.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates generally to receiver systems and methodsfor interference suppression. More specifically, the present inventionrelates to a selective-sampling receiver and methods able to mitigatethe interference in received signals.

2. The Relevant Technology

Transmitting and receiving radio frequency (RF) signals over theairwaves is a vital part of the world today, having wide use in militaryand commercial applications. For example, radar systems at an airportsend and receive signals that are used to track airplanes taking off andlanding. Radar signals are also used to track the movement of armedforces on a battlefield or are used to track incoming enemy missiles orplanes. In like manner, cellular phones use an antenna to send andreceive voice communication signals.

All systems that receive RF signals, from the hand held cellular phoneto the most complex radar system, include a receiver. The receiver isused to process signals received from an antenna. For example, thereceiver may down convert the frequency of the received signals or mayamplify the received signals. The receiver may also be used to sampleportions of the signals. Once the receiver has finished processing thereceived signals, the receiver will generally send the signals to otherequipment and systems such as a signal processor for further processing.

However, the signals that are provided to the receiver often aredistorted by various amounts of signal interference. This interferencemay be from natural causes such as rain or other environmental effects.The interference may also come from other RF signals that have not beenproperly isolated from the desired signal. The interference may even bepurposefully added, such as an interference signal from a radar jammingdevice used in a military application. Interference can prevent areceiver from receiving and interpreting desired signals. As a result,the interference must be dealt with by the receiver or the signalprovided to the signal processor will be distorted.

In the past, many techniques have been used to suppress signalinterference in the receiver. Perhaps the most common is the use of ageneralized side lobe canceller. The generalized side lobe cancelleruses low-gain antennas to isolate the interference signals from adesired signal. Adaptively selected magnitude and phase weights areapplied to the interference signals. These weights are then used toestimate the interference component of the desired signal. The estimatedinterference component is then subtracted out of the desired signal,thus leaving a signal free of most interference.

Another technique that is used in receiver interference suppression isthe co-channel interference mitigation in the time-scale domainalgorithm. This algorithm uses a wavelet transform to estimate andreconstruct the interference from a null space in the desired signal inthe time-scale domain. The estimated interferer is then subtracted fromthe observations and the remaining signal is an approximation of thedesired signals.

These techniques and others in the prior art are able to reasonablysuppress signal interference. However, they are very complex and costly.For example, a large number of antenna arrays may be necessary forinterference estimates. In addition, the receiver requires costlyprocessing abilities for making the interference estimates and thensubtracting them out of the desired signal. The receiver may also needcomplex circuitry to perform the interference suppression operation.Therefore, what would be advantageous is a low complexity receiver withthe ability to suppress interference signals using low cost components.

BRIEF SUMMARY OF THE INVENTION

The forgoing problems with the prior state of the art are overcome bythe principles of the present invention, which relate to a receiver withthe ability to selectively-sample a received signal in order to suppressan interference signal component of the signal while recovering adesired signal component. The selective-sampling may be accomplished bylow cost, low complex analog or digital circuitry. The sampling may alsobe accomplished by digital algorithms.

The receiver includes a first input that receives a first signal. Thefirst signal includes a desired signal component and an interferencesignal component. This first signal may be the summation output of asigma-delta (ΣΔ) beam-forming network

The receiver also includes a second input that receives a second signal.The second signal includes the interference component only. This secondsignal may be the difference output of a ΣΔ beam-forming network whichhas subtracted out the desired signal component.

The first and second signals are provided to sampling circuitry. Thesampling circuitry, which may be analog or digital circuitry, performs asampling operation on the signals. First, the phase of the interferencecomponent of the both the first and second signals is aligned. Next, thepoints in a wave cycle that the interference component of the secondsignal are at a power minimum are detected. Finally, the first signal issampled as close as possible to the point when the second signal is atthe power minimum as the interference component of the first signal willalso be at a power minimum. With the interference component at aminimum, only the desired signal component will be sampled. In this way,the desired signal is recovered and the interference signal issuppressed.

Additional features and advantages of the invention will be set forth inthe description that follows, and in part will be obvious from thedescription, or may be learned by the practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present inventionwill become more fully apparent from the following description andappended claims, or may be learned by the practice of the invention asset forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be discussed withreference to the appended drawings. It is appreciated that thesedrawings depict only typical embodiments of the invention and aretherefore not to be considered limiting of its scope.

FIG. 1A schematically illustrates a ideal selective-sampling receiver inaccordance with the principles of the present invention;

FIG. 1B schematically illustrates a specific analog embodiment of theselective-sampling receiver of FIG. 1A;

FIG. 2 illustrates a flowchart of a method for performing aselective-sampling operation;

FIG. 3A illustrates a desired signal;

FIG. 3B illustrates an interference signal and its power minimums;

FIG. 3C illustrates a summation signal of the signals in FIGS. 3A and3B;

FIG. 4 schematically illustrates a receiver system in which aselective-sampling receiver in accordance with the principles of thepresent invention may be implemented;

FIG. 5 illustrates interference suppression versus channel isolation forvarious angle of arrival;

FIG. 6 schematically illustrates multiple selective-sampling receiversimplemented in a bank configuration with each cell in the bank having aslightly different input relationship;

FIG. 7 illustrates squelch performance of a selective-sampling receiver;

FIG. 8 illustrates a sum/delta without boresite signal; and

FIG. 9 illustrates a sum/delta with boresite signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The principles of the present invention relate to a receiver with theability to selectively-sample a received signal in order to suppress aninterference signal component of the signal while recovering a desiredsignal component. The selective-sampling may be accomplished by lowcost, low complex analog or digital circuitry. The sampling may also beaccomplished by digital algorithms.

The receiver includes a first input that receives a first signal. Thefirst signal includes a desired signal component and an interferencesignal component. This first signal may be the summation output of asigma-delta (ΣΔ) beam-forming network

The receiver also includes a second input that receives a second signal.The second signal includes the interference component only. This secondsignal may be the difference output of a ΣΔ beam-forming network whichhas totally subtracted out the desired signal component.

The first and second signals are provided to sampling circuitry. Thesampling circuitry, which may be analog or digital circuitry, performs asampling operation on the signals. First, the phase of the interferencecomponent of the both the first and second signals is aligned. Next, thepoints in a wave cycle that the interference component of the secondsignal is at a power minimum are detected. Finally, the first signal issampled as close as possible to the point when the second signal is atthe power minimum as the interference component of the first signal willalso be at a power minimum. With the interference component at aminimum, only the desired signal component will be sampled. In this way,the desired signal is recovered and the interference signal issuppressed.

Referring to FIG. 1A, an exemplary selective-sampling receiver system100 in which the principles of the present may be practiced isillustrated. Selective-sampling receiver system 100 is shown by way ofillustration only and is not intended to limit the scope of the appendedclaims. It will become to clear to one skilled in the art from readingthis specification that there are numerous ways to implement theselective-sampling receiver 100.

Selective-sampling receiver 100 includes a first receive input 101 foraccessing a first signal 110. First signal 110 may be a sine wave, asquare wave, a triangular wave, a pulse or any other periodic waveformat any frequency. Selective-sampling receiver 100 takes advantage of theperiodic nature of the input waveform to perform a selective-samplingoperation as will be described in more detail below with respect to FIG.2.

First signal 110 is comprised of a desired signal component and aninterference signal component. First signal 110 may also include othercomponents such as thermal noise. In some embodiments, first signal 110may be the summation output of a sigma-delta (ΣΔ) beam-forming networkas will be described in further detail to follow. However, this is notrequired as first signal 110 may be produced by any means known in theart that combines two or more signal components into a single signal.

Selective-sampling receiver 100 also includes a second receive input 102for accessing a second signal 120. Second signal 120 may also be a sinewave, a square wave, a triangular wave, a pulse or any other periodicwaveform at any frequency. Second signal 120 is comprised of aninterference signal component and may include other signal componentssuch as thermal noise. In some embodiments, second signal 120 may be thedifference output of a ΣΔ beam-forming network as will be described infurther detail to follow. However, this is not required as second signal120 may be produced by any means known to the art.

Selective-sampling receiver 100 further includes sampling circuitry 130.Sampling circuitry 130 is configured to selectively sample the firstsignal 110 so as to suppress the interference component of the signaland thereby recover the desired signal component. Sampling circuitry 130may be implemented by numerous different combinations of analog ordigital components. Advantageously, the selective-sampling operation maybe performed by sampling circuitry 130 components that are lowcomplexity and low cost. It should be noted that selective-samplingreceiver 100 may perform the selective-sampling operation on anyperiodic waveform of any frequency. This includes using theselective-sampling operation in applications such as radar, sonar, andhearing aids. The selective-sampling receiver and the selective-samplingoperation should not be construed to only apply to high frequencyapplications.

For example, sampling circuitry 130 may include delay circuitry 131 foraligning the phase of the interference component of both the firstsignal 110 and the second signal 120. Zero-crossing detector circuitry132 may be used to detect the power minimums of the interferencecomponents during a wave cycle. Sample-hold circuitry 133 may be used tosample the first signal 110 at the proper time. In FIG. 1, sample-holdcircuitry 133 is depicted as a switch that closes whenever zero-crossingdetector 132 detects a power minimum. Sampling circuitry 130 may alsoinclude other components such as inverters, amplifiers for signalamplification, resistors, filters, and the like. As mentioned, there arenumerous circuit component implementations of selective-samplingcircuitry 130.

FIG. 1B illustrates a specific analog implementation ofselective-sampling receiver 100. This specific implementation is by wayof example only, and should not be read to limit the claims. Asmentioned previously, one skilled in the art will appreciate that thereare numerous different circuit implementations of selective-samplingreceiver 100. As will be obvious from FIG. 1B, all of the components ofthe specific analog implementation of selective-sampling receiver 100are low complexity, low cost consumer electronic components that may beeasy implemented.

Specific analog implementation of selective-sampling receiver 100includes elements 150A and 150B that may correspond to delay circuitry131 of FIG. 1B and is used to align the phases of the interferencecomponents. Diode 160 acts as the zero-crossing detector 132 and thesample-hold circuitry 133. In this example, the diode 160 responds toabsolute biasing and produces gain when the second signal is morenegative than the first signal, which is the inverse of the desiredrelationship. As a result, the first and second signals may be rectifiedin some embodiments. This occurs during the negative cycle of thewaveforms.

Operational-amplifier 161 is used to bias the diode to avoidnon-linearity's that might otherwise be produce during sampling. Whenthe magnitude of the first signal is greater than the magnitude of thesecond signal, which occurs at the power minimums of the second signal,diode 160 will not conduct and resistance in the feedback loop ofoperational-amplifier 162 will be high. This provides timing for thesampling that effectively blocks the interference component of the firstsignal and allows gain for the desired signal component from operationalamplifiers. Alternatively, when the magnitude of the second signal isgreater than the first signal, then diode 160 conducts and a gain of oneor unity is added to the signal. Various resistors are also used in thisimplementation for signal control, by producing a mirror image of theunity gain signal that when added, cancels the unity gain signal out.

This circuit may be tuned, if necessary, by attenuating the firstsignal, thereby decreasing the amount of time that the amplitude of thefirst signal exceeds the amplitude of the second signal. However, as thefirst signal is attenuated, the circuit will suffer from decreasedsignal to noise ratio since noise from the second signal is imprinted onto the output of the circuit. However, the output can be used to triggerthe digitalization of the first signal, allowing for reconstruction ofthe desired signal that is then passed on. As the first signal becomesmore attenuated, the timing resolution of the selective-samplingincreases.

This circuit may also be used with multipath and/or pulsed signals. Thesystem described above will produce continuous output of a bore-sitesignal in the absence of any overpowering multipath or jamming signal.This means that the first part of the accessed first signal is passedsince it is at bore-site. When a multipath signal is present, thecomposite signal will tend to pull the desired signal off of bore-siteresulting in the squelching of the channel. If necessary, the pulses canbe filtered out if needed for a specific application.

As has been mentioned, the selective-sampling receiver 100 is configuredto perform a selective-sampling operation using the selective-samplingcircuitry 130 for the digital implementation. The selective samplingoperation may also be performed by a digital algorithm. Referring toFIG. 2, a method 200 for a selective-sampling receiver to perform theselective-sampling operation is described. The method 200 will bediscussed with reference to the selective-sampling receiver of FIG. 1.The selective-sampling receiver accesses a first signal comprising adesired signal component and an interference component (201) andaccesses a second signal, either from an external source or an internalsource, comprising an interference component (202). As can be seen inFIG. 2, the order that the selective-sampling receiver accesses the twosignals is unimportant to the principles of the present invention,although in many embodiments the two signals will be accessed orreceived simultaneously.

Selective-sampling circuitry in the selective-sampling receiver, such asdelay circuitry 131, aligns the phase of the interference component ofboth the first and second signals (203). The selective-sampling receivertakes advantage of the fact that the interference component of the firstsignal may lead or lag the interference component of the second signalby a phase of 90 degrees in some embodiments. By delaying either thefirst or the second signal by 90 degrees, the phase of the interferencecomponents in both the first or second signal should be aligned.

The selective-sampling circuitry then determines when the interferencecomponent in the second signal is at a power minimum during a wave cycle(204). As the first and second signals are usually periodic, they willhave predictable power minimums or zero crossing points. For example, asine wave has two power minimums or zero crossing points per wave cycle,which is referred to the Nyquist sampling rate. The selective-samplingcircuitry, such as zero-crossing detector 132, detects when the secondsignal has the power minimums. Since the interference components of thefirst and second signals are aligned, the interference component of thefirst signal will be at a power minimum whenever the second signal is ata power minimum.

The selective-sampling circuitry samples the first signal as close aspossible to the point in time that the second signal is at a powerminimum (205). The sampling may be accomplished by the sample-holdcircuitry 133 of FIG. 1A. As mentioned previously, the interferencecomponents of both the first and second signals will be at a powerminimum at the same time when their phases are aligned. Consequently,only the desired signal component and perhaps a noise component of thefirst signal will remain to be sampled if the sampling occurs during thepower minimum of the second signal. As a result, any signal that isreconstructed from the sampling will be very close to the desiredsignal. As long as the sampling is performed at least at the Nyquistsampling rate of the first signal, then a reasonable desired signal maybe reconstructed. The reconstructed signal may then be provided by theselective-sampling receiver to other instruments, such as a signalprocessor in a radar system, for further use and analysis.

Advantageously, the selective-sampling method just described suppressesthe unwanted interference signal component and recovers the desiredsignal component without the need for time consuming calculations todetermine interference estimates and then to subtract them from thedesired signal. In addition, since the selective-sampling receiverderives when to sample from the power minimums of the interferencesignal component in real time, it is able to respond to changes in theinterference environment almost instantaneously.

A specific example of the selective-sampling operation will now bedescribed with reference to FIGS. 3A, 3B and 3C. In FIG. 3A, a 450degree portion of a desired signal 302 at bore-sight is shown. Abore-sight signal is one that is directly in front of an antenna and hasmaximum power. The desired signal has a 360 degree cycle and has powermaximums around 135 degrees and 315 degrees. The amplitude at thesepoints is between 0 and 0.1768 in this example.

FIG. 3B depicts a 450 degree portion of an interference signal 304. Theinterference signal has power maximums around 90 and 270 degrees, whichhave amplitude of around 1 and, in this example, power minimums at 0 and180 degrees. There is also a power minimum at 360 degrees, which is thestart of a new wave cycle. Note that during the 450 degrees that areshown, the magnitude of the interference signal 304 is much greater thanthe magnitude of the desired bore-sight signal 302 and would thusdominate the desired signal 302.

FIG. 3C depicts a signal 306 that is a summation of the desired signal302 and the interference signal 304. This may represent the first signalof FIG. 1A. As can be seen, the magnitude of the summation signal 306 isclose to the magnitude of the interference component as the interferencecomponent dominates the signal. FIG. 3C also shows sampling points A, B,and C. Sampling point A corresponds to the power minimum of theinterference component at 0 degrees, sampling point B corresponds to thepower minimum at 180 degrees, and sampling point C corresponds to thepower minimum at 360 degrees.

When the summation signal is sampled as close as possible to thesummation points, the desired signal may be recovered. The recoveredsignal is depicted by the dashed line 308 in FIG. 3C. As can be seen,the recovered signal (dashed line 308) closely mirrors the originaldesired signal 302 of FIG. 3A.

Referring to FIG. 4, a two channel receiver system 400 in which aselective-sampling receiver in accordance with the present invention maybe implemented is illustrated and will now be described. Receiver system400 includes antenna and steering section 410, a ΣΔ beam-former 420, aselective-sampling receiver 430, and a quadrature down converter 440.

Antenna and steering section 410 includes two antenna elements 411A and411B that are used to measure two signals. Antennas 411 may be anyantenna known in the art, such as for example a monopulse antenna array.For example, antenna 411A may be used to measure a signal containingboth the desired signal and the interference signal while antenna 411Bis used to receive the same signal, but at a different phase angle. Themeasured signals are passed through band pass filters 412A and 412B,which are used to filter out unwanted signal bands and may be any filterknown in the art. The filtered signals are then steered by steeringnetworks 413A and 413B, which may be any known steering network in theart, to the inputs of ΣΔ beam-former 420. In the depicted example,steering network 413A is used to steer one of the measured signals tothe bore-sight angle of arrival, while steering network 413B is used tosteer the other measured signal to some off bore-sight angle of arrival.

The ΣΔ beam-former 420, which may be any ΣΔ beam-former known in theart, has a summation channel 422 and a difference channel 421. Thesummation channel 422 produces a first signal which is a composite sumof the desired signal component and the interference signal component.On the other hand, the difference channel 421 produces a second signalwhere one-half of the received signal is subtracted from the other half.However, when the second signal is at bore-site, the desired signalcomponent is phased out, thus leaving only the difference component inthe second signal.

The first and second signals are then provided to selective-samplingreceiver 430, which may correspond to selective-sampling receiver 100 ofFIG. 1A. However, FIG. 4 depicts an alternative embodiment of theselective-sampling receiver. In this embodiment, both an in-phase andquadrature component of the first signal will be sampled. To preserveall signal information in some instances, it may be necessary toselectively sample both the in-phase and quadrature components of thefirst signal. This helps to prevent loss of signal information andminimize distortion produced in the analog reconstruction process. Thesampling circuitry components of selective-sampling receiver 430 will bethe same or similar to those described above in relation to selectivesampling receiver 100.

For the in-phase sampling, the second signal passes through delaycircuitry 431, where it is delayed in order to align its phase with theinterference component of the first signal in the manner previouslydescribed. The zero-crossing detector circuitry 432 then detects whenthe second signal is at a power minimum during a wave cycle. Thesample-hold circuitry 433 then samples the first signal, producing asignal that suppresses the interference and recovers the desired signal.

For the quadrature sampling, the first signal is passed through animpedance inverter 435, which creates a quadrature component of thefirst signal. The second signal is passed through circuitry 438, whichcreates a quadrature component of the second signal and aligns thephases of the signals. The zero-crossing detector 436 detects when thequadrature second signal is at a power minimum during a wave cycle. Thesample-hold circuitry 437 then samples the quadrature first signal,producing a signal that suppresses the interference and recovers thedesired signal.

Both the in-phase and quadrature sampled signals are then passed toquadrature downconverter 440. Both signals pass through low-pass filters440A and 440B in order to remove harmonic content introduced in thesampling operation. Some local oscillation 441 is mixed by mixers 443Aand 443B with the in-phase and quadrature signals respectively, thelocal oscillation having been converted to quadrature by impendenceinverter 441 before the mixing. Finally, the adder circuitry 445combines the in-phase and quadrature signals to reconstruct the desiredsignal.

The two channel receiver system just described suppresses interferencewithout the need for complex circuitry. Cross talk between the summationand difference channels in the ΣΔ beam-former, however, may limit thesuppression of the interference. However, providing isolation for thetwo channels helps to overcome this problem. The isolation may beaccomplished by any isolation technique known to one skilled in the art.FIG. 5 shows interference suppression versus the angle of arrival of theinterference signal for various levels of isolation in the beam-former.For example, curve 501 illustrates interference suppression for 20 dB ofisolation, curve 502 illustrates interference suppression for 30 dB ofisolation, curve 503 illustrates interference suppression for 40 dB ofisolation, curve 504 illustrates interference suppression for 50 dB ofisolation, and curve 505 illustrates interference suppression for 60 dBof isolation. In some embodiments, the selective-sampling receiver 100may be utilized in a bank of multiple selective-sampling receivers. Thisis done to increase the field of view that may be monitored by a systemimplementing the selective-sampling receivers as the measured azimuthand elevation angles are increased. This is illustrated in FIG. 6, whichdepicts a bank 601 of 16 selective-sampling receivers or filters. Inthis embodiment, the first signal comprising the interference anddesired signal components is still measured at bore-sight as in the twochannel case and is provided to all 16 selective-sampling receivers. Thesecond signal consisting of the interference signal, however, is shiftedfor every selective-sampling receiver, 1 degree in the depicted example,such that the interference component is slightly different for eachreceiver. The sampling operation will still be performed as describedpreviously, i.e. the first signal will be sampled when the interferencecomponent of the second signal is at a power minimum.

The selective-sampling receiver also may be implemented in a system thatuses a sub-array to measure an antenna beam. In this case, only the evenside lobes will have a receiver in-lobe condition. As a result, asquelch region will be provided for the odd side lobe energy. Inaddition, a squelch region is produced and there is no output when thedelta input is of a greater value than the attenuated sum input. Thiscan be seen in FIG. 7. In FIG. 7, the main beam 701 shown with thesquelched lobe 702. This embodiment may be useful in preventinginterference from electronic counter measures that often time enter themain lobe from the side lobes.

The selective-sampling receiver and selective-sampling method describedwith relation to FIGS. 1A, 2, and 4 above are useful in counter-countermeasure systems that are used to block electronic counter measures andtracking systems that are used to suppress decoy signals. In particular,the ability of the selective-sampling receiver to adjust almostinstantaneously to a change in the interference environment can behelpful in a situation where a radar jamming signal is present in orderto prevent a target from being seen. This ability is also helpful todiscriminate between a target and a decoy, for example an airplane usingradar, a ship using sonar or submarine pulling a decoy to deflectdetection by radar or sonar.

The selective-sampling receiver and selective-sampling method describedwith relation to FIGS. 1A, 2, and 4 above may be utilized in manymedical applications. For example, the selective sampling receiver maybe used in ultrasound systems. An ultrasound transducer is a series ofpiezoelectric transducers placed in parallel with each other. As a soundpulse is sent out it travels at the speed of sound until it hitssomething such as soft tissue. It then reflects some of the energy,which is picked up by the ultrasound transducer. Each piezoelectricsensor picks up some of this received energy and a computer processingan image is formed. The selective sampling receiver helps to focus thereceived energy for better imaging.

Likewise MM systems pickup radio frequency energy in order to form itsimage. When water atoms are placed in a strong magnetic field the atomsalign to the same orientation. When this water is pulsed with RF energy,the atoms shift alignment to respond to the RF pulse similar to amicrowave oven. When the RF energy stops, the water realigns to themagnetic field and in the process releases RF energy as well. Thisenergy is read and an image is formed. Different densities of waterrelease different amounts of RF energy which look different on the finalimage. The selective sampling receiver is capable of focusing in onsmaller areas of interest or increase the resolution in troughs areas.In addition, since more than one thing can be seen at the same time inthe same field of view higher resolution images are possible.

The selective sampling receiver may also be used in hearing aids andother such devices. In a hearing aid or other repeater applications, thesecond signal may be produced by the system itself. This means that theinformation that is obtained from the second signal discussed previously(i.e., when to sample and the zero-crossing point of the second signal)can be predicted by the system. As a result, only a first signalcontaining both an interference and desired signal component is actuallyaccessed or received by the hearing aid. However, since thezero-crossing point is predicted for the interference component, thedesired component is sampled as previously discussed and the desiredsignal can be produced.

The selective-sampling receiver and selective-sampling method describedwith relation to FIGS. 1A, 2, and 4 above may also be utilized incommunications networks. Because the selective sampling receiver has theability to suppress unwanted signals, two satellites or communicationtowers may be in close proximity to each other and transmit using thesame frequencies. Since each satellite or communication tower will haveits own selective sampling receiver, the amount of data that may betransmitted is increased as each satellite or communication tower willsuppress unwanted signals from the other satellite or tower.

Accordingly, the principles of the present invention relate to aselective-sampling receiver and method. The selective-sampling receiverutilizes low complexity, low cost components to achieve a high level ofinterference signal suppression. This removes the need for expensivehardware to be used in interference suppression. In addition, the needfor complex possessing capabilities is also removed. Accordingly, theprinciples of the present invention are a significant advancement in theart.

In order to find the right time to sample a signal that is made up ofmore than one component (a desired signal and at least one interferencesignal) resulting in the separation of one of the components, antennascan be sued to pick up patterns that have nulls. The desired signal isplaced in this null in the antenna or an antenna network pattern meaningthat this antenna has no input from the desired signal. A second antennaor antenna network will have the desired signal in its antenna patternalong with the interferer.

One such system is a monopulse antenna array. Two antennas create thisantenna network. Two channels are created; one is called the sum channelsince antenna elements A and B are added up in it. The second channel iscalled the Delta channel since one half of the received signal issubtracted from the other half. For example input A is subtracted frominput B. A-B and the radio frequency pickup patterns as compared toangle of approach of RF energy can be determined. A signal that is atbore-site (directly in front of the antenna array) has maximum input inthe Sum channel. But since the inputs are matches in all antennapickups, the delta channel has no pick up of the signal since antenna Acompletely subtracted from antenna B.

Now using the delta channel that has only the interferer signal, thepoint in time to sample the sum channel that has the interferer and thedesired signal can be determined.

In one embodiment, a satellite dish Gain of the desired signal fromcompeting satellites is 10-20 dB. In the selective sampling receiverthis separation in amplitude isn't created with satellite dish gain butin interference suppression ending with an equal amount of amplitudedifference in the final product. Two satellites can now exist in closeproximity operating on the same frequency and not interfere with oneanother using embodiments of the invention. Advantageously, the datathroughput may be doubled when dealing with properly designed systemutilizing embodiments of invention described herein.

Embodiments of the invention can be used with any type of waveform(sine, square, triangle, pulse, etc.) and any transmission medium (air,water, electromagnetic, etc.) to detect energy levels of thesewaveforms. Sampling can be accomplished during the representative powerlevels taken from the waveform.

With repetitive sampling of a waveform, the waveform can be convertedinto a steady power level. This may include multipath signals althoughthe exact power level may not be known. Fluctuating power levels may bedue to background signals that are not synced to the detected orpredicted waveform and resulting sampling points. Separation of thesefluctuating levels can be done mathematically or with a filter such as acapacitor. When a waveform is held to a steady power level, weakerwaveforms can be detected and received. Alternatively, known orsampled/detected sources of interference can be sampled such that theydo not appear in the final sampled output.

By sampling as discussed herein, a signal can be produced that issuppressed. This allows for the same frequency to be used for bothreceiving and transmissions. This may be used, by way of example and notlimitation, in repeaters and hearing aids. When sampling isaccomplished, it is preferably done at twice the primary frequency ortwice the intermediate frequency or twice the received frequency. thisis above the Nyquist sampling rate. Further, embodiments of theinvention can quickly respond to changes in the interfering signal sinceit is one half of the received wavelength.

Placing the signal of interest or the desired signal into an amplitudenull on an antenna or an antenna array or other device or system whichproduces a receiving/pickup signal, the undesired signals can beminimized for a minimum or constant or known energy point at whichsampling is accomplished. In one embodiment, the signal of interest andthe undesired signal are offset in the pickup system such that theundesired signal is present and the desired signal is not.

After analyzing the undesired signal or signals for the proper timing,which is preferably located at the minimum energy points or any known orconstant energy points. In some embodiments, a phase delay may be neededin order to accomplish sampling at the same point of time when referringto the phase of the undesired signals.

In one embodiment, to avoid the un-uniformed multiple signal addition ofthe undesired signal that occurs when producing an antenna's null ascompared to an omni directional antenna's addition of the same signalscoming from different angles of approach, a purely null or delta antennasystem pickup system can be used. In such a system, the signal ofinterest is placed into the true null for interference analyzing. Thesignal of interest is then sampled out of the two null channels that areoffset from the signal of interest in opposite directions ororientations when compared to the graphed null pickup patterns. Theoutput of these two pickups is full wave rectified or changed to anabsolute value and added. The provides for a suppressed, but presentsignal of interest and a uniformed pickup pattern for the signal ofinterest and the interfering signals that are analyzed in the true deltapickup pattern, except close to boresight or the center of the dualdelta pickup patterns. This eliminates the ambiguities that form fromusing unlike system channels that have different pickup patterns.

Sinusoidal thermal noise signals can also be suppressed due to the samesignals being used throughout with small delays added to provide fordifferent angles of approach. As the channels are compared to each otherthey will be similar and the point of suppression for this noise can befound. As a result the system signal to noise should at least remainconstant as it passes through the system.

One embodiment uses the angle of approach to isolate the signal ofinterest and such systems are inherently directional. When enough energyis received from phase analyses for the unwanted signal, the unwantedsignal will be suppressed from off null angels of approach. This allowsfor added angle accuracy to be achieved.

An analog or digital algorithm that compares received levels fromdifferent channels such as a sum and difference channels of a mono-pulsereceiver system where the signal of interest is placed in a null so thatwhen this channel passes through its zero crossing the sum channel issampled.

A bank of analog circuits/digital algorithms where the input to eachcell in the bank is formed to represent a different angle of approachresulting in a wide field of view. Multiple returns are processed in aparallel process of evaluation allowing for faster evaluation of thereceived wave front.

Counter-counter measure systems may utilize large energy returns(jamming of interference) or numerous radio echoes (balloon or decoys).Because one embodiment of the invention uses an operational amplifier, adiode and a few resisters, it is less likely to be affected by highenergy particles as found in space that will damage large integratedcircuits such as signal processors. This analog suppression of theunwanted signals and reception of wanted signals can be performed fast.

Tuning of such an analog system in regards to sensitivity to angle ofapproach is accomplished by attenuation of the channel in which thedesired and undesired signals are placed. Now when the amplitudes arecompared in the two channels the desired signal should be larger inorder to come out of the comparator. Signal to noise degradation can beovercome if sampling is done from the un-attenuated channel before it isattenuated.

A receiver can take advantage more than one transmitter in the antennasfield of view but use the tuning to separate out the differenttransmitters. This can allow for more than one satellite to be in asatellite receivers/dishes field of view and yet have the receiverchoose which transmitted signal to pass on for processing.

When one embodiment of the system is tuned, the signal output may beeither a sinusoidal signal if the signal of interest is in it or noiseif the signal of interest is not in it or is two small to overcome thenoise floor.

In one embodiment, it is possible to squelch out unwanted signals bymanipulating the pickup patterns so that the desired angle of approachis passed but unwanted or undesired angles of approach are squelched.This is accomplished by overlapping the pickup patterns such as arraysof different sizes such as a full size into the sum input and half thesize into the delta input in a mono-pulse system. As a result the oddsidelobe are squelched.

In pulse systems or spread spectrum systems this approach can be usedand the need for very accurate timing systems eliminated. This is doneby utilizing the angle of approach. The first signal will pass from theangle of interest but multi-paths come from different angles of approachthat will pull the received signal out of the angle bin being used. As aresult the first leading pulse will be passed and other paths cansquelch the channel.

The Handling of Multiple Interferes

When just one jamming/interfering source is presented in a SelectiveSampling Receiver's Delta Channel the receiver operates in the amplitudedomain. Embodiments of the invention can also operate when the sum anddelta system has two jamming/interfering sources. In this case, it ispossible for the two or more sources to have different amplitudes in thesum and delta channels. The zero crossing of the combined sine wave canbe dependent on amplitude and phase/frequency of the two interferingsignals. In this case, embodiments of the invention can change to thefrequency domain by demodulating frequency modulated signals from therespective Sum and Delta channels. This eliminates any problemsassociated with amplitude summing of the multiple jamming or interferingsources.

I one embodiment, the invention may start by limiting the amplitudeentering into the frequency domain. This reduces the affect ofatmospheric noise that appears as pops or hisses in AM AmplitudeModulated systems.

One advantage of frequency modulation is that it is free from theeffects of atmospheric noise or “static” that affects only the amplitudeof the wave, since all the information is in the frequency variations.If the modulation is removed and the amplitude of the signal is varied,the ratio detector is advantageously not sensitive to the level. Some FMdemodulators respond to the amplitude as well as the frequency, so thesignal may be limited before detection. However, this is not necessaryfor a ratio detector.

FIG. 8 illustrates one embodiment of an approximate amplitude andfrequency summation 800 that would found in the different channels. Notethat the amplitudes changed but the frequency did not. This illustratesthat when two interfering signal sources and no boresite signal ispresent in the sum channel 802 and delta channel 804, the frequencydemodulated signals will be the same. As a result both interferingsignals will be suppressed by using the time domain suppressiontechniques described herein.

Now when a signal is added at boresite, this signal contributes to thedemodulated FM spectrum of the Sum channel 902 but not to the Deltachannel 904 as seen in FIG. 9 at 900.

The demodulated Sum channel 902 is offset directly by the FM propertiesof the boresite signal source. As a result, a boresite signal can beseen in the presence of multiple off-boresite signal sources.

As a result, it may be useful to include not only Frequency andAmplitude Modulation techniques but Phase, Pulse, or any modulationscheme any domain or practice that is used to convey or measureinformation. This may include at any RF radio frequency, IF intermediatefrequency, base band, or data stream of any kind whether created by WTIintentionally, as the case of broadband jamming or unintentionally as isthe case of unintended interference.

It may also include recovered interference of any kind through any typeof system that creates a system in which the desired information is inone channel with the interference, and only the interference in theother channel.

An imaging system using a multi-element array that creates one or morepencil receiver beams that can be used to scan for RF sources orreflections of RF signals is within the scope of the invention. Such asystem can be used for navigation during bad weather or in completedarkness. When used in aviation, a runway can be lined with low powertransmitters that such a system can see the runway. In addition, therunway can be illuminated with an RF beam of energy so that you can seereflection of objects that may be on the runway.

Furthermore, forward looking radar systems can be made or transmitterscan be collocated with beacon lights. If a geological survey was done ateach such beacon/transmitter the surrounding landscape can be simulatedout of a database and presented to the pilot. And time stamp and ID fromeach transmitter may be needed.

In one example, such as with IED (Improvised Explosive Device), it isnecessary to generate an interfering signal LED's are often detonatedwhen a signal (such as from a cellular device) is received by the IED.The interfering signal (such as a broadband signal) is being generatedas increasing strength in order to compensate for improvements to theIEDs. One drawback to this approach is that the generated interferingsignal now interferes with other communications.

Embodiments of the invention can overcome this problem by simply usinginformation about the interfering signal, which is shown in thisspecific example. This information can be communicated in any way,optically for example. Timing differences can also be accounted for. Inthis case, knowing the interfering signal allows the desired signal(such as communications among the various entities) to be recovered. Infact, because the interfering signal is known, efficiencies in recoverycan be achieved.

More particularly, in the TED environment the jammer signal (orinterfering signal) is not necessarily picked up but rather communicatedto the receiver because it is known, which would provide even greaterchannel isolation, and greater performance. This communication can be asignal pickup such as through an antenna, data link in any form, or asynchronizing/timing pulse that synchronize the two systems. Any type ofsystem that will communicate enough information to find the phase of theunwanted signal is within the scope of the invention.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. A receiver system for selectively sampling a signal with two or moresignal components, the receiver comprising: a first receive input foraccessing a first signal, the first signal comprising a first desiredsignal component and an interference signal component; and samplingcircuitry coupled to the first input, wherein the sampling circuitryrecovers the first signal from the interference signal component byidentifying when the interference signal is at a power minimum using atleast frequency demodulation.